Method for manufacturing coloring ceramics via colloidal dispersion followed by conventional pressing techniques

ABSTRACT

A colored ceramic powder is produced from a mixture of coloring solutions consisting of metallic salts that are introduced to a ceramic slurry and subsequently dried. The coloring solution may comprise for example of chosen metallic salts, a solvent, an organic solvent such as derivatives of propylene oxides, an acid and a possible binder. Once all the constituents are thoroughly mixed to a homogeneous state, the slip is dried to a powder form, which spray drying equipment can be used. The dried powder can then be subjected to an isostatic or biaxial press manufacturing process to create a green state ceramic body. Once pressed, the ceramic body can be subjected to a sintering process. After final sinter, the resulting ceramic body possesses an innate color that is homogenous throughout its composition. The method is especially useful for coloring zirconia dental restorations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of, and claims priorityto, U.S. patent application Ser. No. 13/659,209, filed on Oct. 24, 2012which, in turn, is a continuation-in-part of U.S. patent applicationSer. No. 13/410,251, filed Mar. 1, 2012, which issued as U.S. Pat. No.9,365,459, which are all hereby incorporated by reference in theirentireties.

FIELD OF THE INVENTION

The present invention relates to the process in which a color solutionconsisting of metallic salts is introduced to a ceramic slurry andsubsequently combined with a binder, dried, pressed into a green stateand sintered.

BACKGROUND ART

Current techniques for coloring ceramics have limitations due toprocessing. At present, methods involve dipping a pre-sintered ceramicbody into a coloring solution containing metallic salts. Such methodsmay often result in inhomogeneous coloring on the surface of theceramic. In addition, the penetration of the coloring solution into thepores of the ceramic is largely affected by the components, composition,and properties of the solution. Depending on the constituents present inthe solution, little or no color penetration can result.

Such disadvantages arise when attempting to color a pre-sinteredceramic. This has prompted the need for an alternative method to color aceramic body. Such a method will remove the need to color a pre-sinteredceramic body and will result in a ceramic with innate color aestheticsthat are homogenous throughout the ceramic both internally and on thesurface. The present invention relates to creating a colored ceramicduring a slip casting process in which a color solution consisting ofmetallic salts is introduced into the slip and subsequently combinedwith a binder, dried, pressed into a green state and sintered.

Current methods for coloring ceramic bodies involve dipping apre-sintered ceramic of final shape into a coloring liquid. Theseprocesses require a wide range of soaking times and drying times toensure uniform and good quality results. After dipping, the ceramic bodyis dried and sintered, after which the final color is achieved.

The dipping methods currently used depend largely on the capillaryaction of the coloring liquid and the infiltration of said liquid intoceramic pores. The properties of the coloring liquid, such ascomposition, concentration, viscosity, pH, surface tension and wettingability directly influence the performance of the liquid. Should anyproperty not be optimized, undesirable results such as disproportionatecoloring or poor penetration of color into the ceramic body may result.

These methods color ceramic bodies after the ceramic has already beenprocessed and fabricated. The coloring agent is added to the ceramicsystem after initial fabrication of the ceramic. Therefore, the color isnot innate to the ceramic.

SUMMARY OF THE INVENTION

The present invention relates to a process for coloring ceramics bycolloidal dispersion. It is during this slip casting that a coloringsolution consisting of metallic salts is introduced to the slurry andsubsequently combined with a binder, dried into a pressable coloredpowder, pressed into a green state and sintered.

A coloring solution may comprise for example a metallic salt, a solvent,an organic solvent such as derivatives of propylene oxides, and an acidcan be introduced to the slip casting process.

Such a coloring solution can be added to the slip. The solution isthoroughly mixed with the ceramic slurry, after which the ceramic bodyis combined with a binder, dried and finally subjected to a sinteringprocess.

After final sinter, the resulting ceramic body possesses an innate colorthat is homogenous throughout its composition.

The present invention utilizes metallic salts as the coloring agentpresent in the coloring liquid that is added to the slip. The primaryproperty of the metallic salt is such that is soluble in the solvent.

Metallic salts of transition metals from groups 3-12 on the periodictable can be used for the coloring solution. In addition, salts fromrare earth metals can be used as well. Metallic salts in the forms ofoxides or containing anions such as: Cl⁻, SO₄ ⁻, SO₃ ⁻, Br⁻, F⁻, NO₂ ⁻,and NO₃ ⁻ may be used.

The coloring solution, as it relates to the process by which a coloredceramic is made via colloidal dispersion, should contain metallic saltsin the range of 0.01% to 5% by weight. The concentration of the metallicsalts is directly dependent on the target color that is to be achieved.

A preferred coloring solution also contains an organic solvent. Thepurpose for this solvent is to assure the homogeneity of the solutionthat contains the metallic salts. Derivatives of polypropylene oxide canbe used for this purpose.

The coloring solution, as it relates to the process by which a coloredceramic is made via a slip, should be comprised of an organic solvent of1% to about 10% by weight and a binder of 0.5% to 10% by weight.

A preferred coloring solution also contains acid. The purpose of thiscomponent is to maintain the colloidal stability of the coloringsolution when mixed into the ceramic slurry by upholding a stable pH. Anacidic pH level in the range of 1.0 to 4.0 is ideal.

The coloring solution, as it relates to the process by which a coloredceramic is made via colloidal dispersion, should be comprised of an acidof 0.05% to about 5% by weight.

The primary property of the solvent is that it can dissolve the metallicsalts and facilitate a homogenous solution. Solvents can include water,alcohols, ketones, organic solvents, or mixtures thereof. The solventcomprises the majority of the solution by weight.

The present invention encompasses the process by which the coloredceramic is fabricated. Due to the unique properties of color thatincludes hue, chroma and value, varying ratios of coloring liquid areadded to the ceramic slurry before the slip casting process. The ratiois directly dependent on the target color that is to be achieved.

The colloidal slip, as it relates to the process by which a coloredceramic is made, should have a ratio of grams of coloring liquid pergram of ceramic slurry in a range of about 0.01 to about 1.00.

The present invention may be employed in the fabrication of a coloredceramic using a unique colloidal mixing process of a coloring agent intoa ceramic slurry. The coloring liquid is added to the ceramic slurry andafterward mixed to assure that a homogenous mixture is attained. Theslurry mixture is then combined with a binder, dried into a powder,pressed into a green state and sintered.

After final sinter, a homogeneously colored ceramic body results.

An object of this invention is to create a ceramic body with a color ofspecific hue, chroma, and value. A further object is to create a processthat allows for a multitude of colors to be achieved.

Still a further object is to create a process that allows for thefabrication of a ceramic body with a homogeneous and uniform colorwithout adverse effects on the mechanical and optical properties of theceramic.

Still a further object is to create a coloring solution designed for theceramic fabrication process that results in a uniformly colored ceramic.

DETAILED DESCRIPTION

The present invention relates to color a ceramic body during the initialprocess and fabrication of the ceramic. A coloring solution is added tothe ceramic system during the processing stage. The result is a ceramicwith intrinsic color properties and complete color saturation.

A color solution of known compositions and concentrations can be used tocreate any color of desired hue, chroma and value. Using metallic saltsas the coloring agent, as well as a solvent to disperse the salts intosolution, this invention relates to a process that is designed forcoloring a ceramic during the manufacturing process of the material.

The process hereof ensures total and homogeneous color penetration intoa ceramic body. Such a ceramic body can then be cut or milled into anyshape or form. The final sintered ceramic body will be coloredcompletely without the need for an extra coloring process that normallytakes hours using conventional ceramic color methods.

The coloring solution and process hereof do not adversely affect themechanical and optical properties of the natural ceramic. Because thecoloring agent is mixed in a colloidal process, the coloring ions arehomogenously distributed through the ceramic's crystal structure.Therefore, the coloring ions are incorporated throughout the ceramic.

Application

The present invention relates to the fabrication of a colored ceramicusing a unique colloidal mixing process of a coloring agent into aceramic slurry. Such a process can be applied to the dental industry,particularly in the fabrication of dental zirconia. At present, zirconiablocks are fabricated for the milling of dental crowns, bridges andcopings. Due to the natural strength and aesthetics of teeth, suchmechanical and optical properties are needed in dental ceramics.

At present, dental frameworks are milled from zirconia blocks. Becausethe natural color of zirconia is white, there is a need to color theceramic. The ceramic is therefore colored using conventional dippingmethods using coloring liquids. Current methods involve dipping apre-sintered zirconia framework of final shape into the color liquid fora specified soaking time period. Frameworks are subsequently dried andsintered. The dental industry at large uses the VITA classic shade guideas a standard for teeth aesthetics. These colors are unique in hue,chroma and value. Conventional color liquids are made to match theseproperties.

The present invention can eliminate the need for the coloring process ofthe pre-sintered dental frameworks. A zirconia dental ceramic can befabricated with the innate color properties of the final desiredproduct.

It is within the scope of the present invention to fabricate a dentalzirconia ceramic with a color that matches the hue, chroma and value ofthe VITA Classic dental shades.

It is also within the scope of the present invention to fabricate adental zirconia ceramic block that can be milled to a specified dentalframework of final shape and subsequently sintered. The resultingsintered zirconia framework will be of final shape and color thatmatches the VITA Classic shades.

Testing Results

Successful results have been achieved with the present invention. Acoloring solution of known concentration and composition and mixed itinto a colloidal zirconia slurry was used.

A coloring solution containing TbCl₃, CrCl₃, propylene glycol, 37%hydrochloric acid and de-ionized water was added to a zirconia slurry.

The exact composition of the coloring solution is as follows: 0.0914 wt% TbCl₃, 0.0609 wt % CrCl₃, 2.070 wt % propylene glycol, and 0.104 wt %hydrochloric acid. The balance was de-ionized water. The final pH of thesolution was measured to be 1.93.

A ratio of 0.0218 grams of coloring liquid per gram of zirconia slurrywas blended into a homogeneous mixture.

The slurry was subsequently combined with a binder, dried and pressed.This was followed by a sintering process during which the discs werefired into a pre-sintered bisque stage. After final sinter, the coloredceramic was cut to assure complete color saturation.

Total and homogenous coloring of the ceramic block was achieved. Using aVITA Easyshade instrument, the color was checked to verify if a dentalshade had indeed been matched. The final color matched closely to theVITA Classic shade B2.

A second test was performed to verify the results of the first. Acoloring liquid of different composition and concentration was used forprocessing.

The exact composition of the coloring solution is as follows: 0.122 wt %TbCl₃, 0.081 wt % CrCl₃, 2.030 wt % propylene glycol, and 0.104 wt %hydrochloric acid. The balance was de-ionized water. The final pH of thesolution was measured to be 1.96.

A ratio of 0.0218 grams of coloring liquid per gram of zirconia slurrywas blended into a homogeneous mixture with a binder.

The slurry was subsequently dried and pressed into a disc shape. Thiswas followed by a sintering process during which the discs were firedinto a pre-sintered bisque stage. After final sinter, the coloredceramic was cut to assure complete color saturation.

Total and homogenous coloring of the ceramic block was achieved. Using aVITA Easyshade instrument, the color was checked to verify if dentalshade had indeed been matched. The final color matched closely to theVITA Classic shade A1

Therefore, it will be understood that the present invention, as itrelates to a coloring liquid that is introduced to a colloidal processby which a colored ceramic is fabricated, has proven to be particularlyuseful in the dental industry to create a dental ceramic with intrinsiccolors that match the desired aesthetics of dental frameworks.

It will now be appreciated that the present invention relates to aunique process for providing selected coloring of ceramic materials inpressing fabrication by introducing a coloring solution of metallicsalts into the slurry. This invention is particularly applicable to thecoloring of fabricated zirconia blocks for use as dental restorationssuch as full contour crowns, bridges and the like. While exemplaryembodiments have been disclosed herein, the scope hereof will be limitedonly by the appended claims and their legal equivalents.

We claim:
 1. A colored zirconia ceramic slurry fabricated by a colloidalmixing process comprising the steps of: a) obtaining a coloring solutionconsisting essentially of at least one metallic salt as a coloringagent, a solvent, and optionally, an organic solvent and optionally, anacid, wherein the at least one metallic salt is soluble in the solvent,and wherein the at least one metallic salt comprises metallic salts ofchromium and terbium as the coloring agent; b) choosing the relativeconstituents of the coloring solution to provide a selected color foruse in a zirconia ceramic dental restoration; c) choosing a relativeamount of the coloring solution for an amount of a zirconia ceramicslurry comprising a ceramic material that is predominantly a zirconiaceramic material, to provide a selected color intensity for use in thezirconia ceramic dental restoration; d) mixing the amount of thecoloring solution and the amount of zirconia ceramic slurry todistribute the coloring solution throughout the zirconia ceramic slurry;and e) adding a binder in an amount of from 0.5% to 10% by weight of thecoloring solution, to the mixture of the coloring solution and thezirconia ceramic slurry to form the colored zirconia ceramic slurry,wherein, the colored zirconia ceramic slurry comprises the zirconiaceramic slurry, the coloring solution, and the binder.
 2. The coloredzirconia ceramic slurry of claim 1 wherein the colored zirconia ceramicslurry consists essentially of the ceramic material, the coloringsolution, and the binder.
 3. The colored zirconia ceramic slurry ofclaim 1 wherein the at least one metallic salt consists essentially ofmetallic salts of chromium and terbium as the coloring agent.
 4. Thecolored zirconia ceramic slurry of claim 1 wherein the coloring solutionof step (a) comprises 0.01% to 5% by weight of the at least one metallicsalt.
 5. The colored zirconia ceramic material of claim 1 wherein thecoloring agent comprises CrCl₃ and TbCl₃ in a weight ratio ofapproximately 2 to 3 (CrCl₃ to TbCl₃).
 6. The colored zirconia ceramicslurry of claim 1, wherein the zirconia ceramic slurry of step c)comprises a colloidal dispersion of white zirconia powder.
 7. Thecolored zirconia ceramic slurry of claim 1 wherein the coloring solutioncomprises water as the solvent.
 8. The colored zirconia ceramic slurryof claim 1 wherein the organic solvent is an alcohol or ketone.
 9. Thecolored zirconia ceramic slurry of claim 1 wherein the organic solventis a derivative of a propylene oxide or propylene glycol.
 10. A coloredzirconia ceramic slurry for use in a dental restoration comprising amixture of a) a ceramic material that is predominantly a zirconiaceramic material; b) a coloring solution consisting essentially of asolvent and a coloring agent consisting essentially of metallic salts ofterbium and chromium dissolved in the solvent; and optionally, anorganic solvent; and optionally, an acid; and c) a binder.
 11. A coloredzirconia ceramic powder for use in a zirconia ceramic dental restorationcomprising ceramic material that is predominantly a zirconia ceramicmaterial, a coloring agent consisting essentially of metallic componentsof terbium and chromium to provide a selected color for the dentalrestoration, and a binder.
 12. The colored zirconia ceramic powder ofclaim 11 wherein the metallic components of chromium and terbium arepresent in a weight ratio of approximately 2 to 3 (chromium component toterbium component).
 13. A colored zirconia ceramic body for use inmaking a zirconia dental restoration comprising a green state, zirconiaceramic body consisting essentially of the colored zirconia ceramicpowder of claim 11, wherein the coloring agent is distributed throughoutthe colored zirconia body.
 14. The colored zirconia ceramic body ofclaim 13, wherein the metallic components are present in a weight ratioof approximately 2 to 3 (chromium component to terbium component).
 15. Acolored zirconia ceramic powder for use in a zirconia ceramic dentalrestoration comprising a zirconia ceramic material that is predominantlya zirconia ceramic material and a coloring agent that comprises metalliccomponents of terbium and chromium for coloring the zirconia ceramicmaterial.
 16. The colored zirconia ceramic powder of claim 15 whereinthe coloring agent comprises CrCl₃ and TbCl₃.
 17. The colored zirconiaceramic powder of claim 15 wherein the coloring agent comprises CrCl₃and TbCl₃ in a weight ratio of approximately 2 to 3 (chromium componentto terbium component).
 18. A colored zirconia ceramic body for use inmaking a zirconia dental restoration comprising a millable, pre-sinteredceramic body comprising ceramic material that is predominantly azirconia ceramic material and a coloring agent that comprises metalliccomponents of chromium and terbium distributed throughout the coloredzirconia ceramic body.
 19. The colored zirconia ceramic body of claim 18wherein the coloring agent comprises CrCl₃ and TbCl₃.